Promisify EventEmitter. For awaiting one time events, such as being notified if something is ready

async-emitter.js

/**
 * Create a one-time use Promise invoked by an event emitter
 * Allows for awaiting an event
 */
const asyncEvent = (eventEmitter, eventName) => 
  new Promise(resolve => {
    const resolveFn = (...args) => {
      // remove the listener so the promise is never resolved multiple times
      eventEmitter.removeListener(eventName, resolveFn);
      resolve(args);
    };
  
    eventEmitter.on(eventName, resolveFn);
  })

module.exports = asyncEvent;

example.js

const asyncEvent = require('async-event');

async function start() {
  const emitter = new EventEmitter();
  setTimeout(() => emitter.emit('say', 'World'), 1000);
  
  console.log(`[${Date.now()}] Hello`);
  const [who] = await asyncEvent(emitter, 'say');
  console.log(`[${Date.now()}] ${who}`);
}

start();